Bathroom Ventilation Regulations

[Flyfisher]

I'm in the process of installing an extractor fan for a shower cubicle in a bathroom. The fan has an overrun timer but this feature requires an additional separate power supply to the light fitting, which will be awkward to arrange. I'm therefore proposing to just connect the fan to the light fitting (via an isolation switch mounted outside the bathroom). This arrangement will mean the fan switches on and off with the bathroom light, i.e. will have no overrun.

Does anyone know if such an arrangement is compliant with the building ventilation regulations?

I've scanned through the Part F (2006) document and the only reference I could find to over-running fans is in F1 Table 1 mentions that "For a room with no openable window (i.e. an internal room), the fan should have a 15-minute over-run".

The bathroom in question does have an opening window, so am I safe to assume that an over-run fan is not required under these regulations?

 

[Jill]

I'm sure extractor fans are "supposed" to switch on with the light. We didn't want this in our ensuite so the electrician wired them separately and told us if building regs come, make sure you flick both on together. A work colleague also had your proposed arrangement but got their electrican to alter it so that when visiting the bathroom in the middle of the night the fan doesn't automatically come on.

In the bathroom we have an external switch for the fan which is also connected to the light, the fan switch can then be switched on or off, so only comes on with the light when you want it to. The bathroom fan overruns for quite a while after the light has been switched off but I've never timed it , i'll be having a shower soon so i'll time it for you.

 

[skier-hughes]

We have an opening window

 

[Flyfisher]

To be honest, I'm not overly fussed about meeting the regs (none of the other work is under BC ) but I thought that if I'm going to the trouble of installing an extractor fan then it might as well be compliant. But the wiring arrangement is such that although it is very easy to connect the fan to the light, there is no convenient source of unswitched power that would allow the fan to overrun.

I decided to install a fan because I want to minimise condensation from the shower and opening the window won't always be convenient as the room in question is on the ground floor.

I think I'll just connect the fan across the light, operate it from the lightswitch and ignore the overrun feature. The fan will have an isolator switch outside the room, so it can be separately switched off if necessary.

 

[robgil]

if it were me and i was starting a fresh id install a fan with a movement sensor on it so it will come on when some one is in the room regardless of the time of day. i never really seen the point of an extractor that only works when you put the light on unless you have a very dark bathroom or one with no windows.
this type of fan might be easier to install as well because you have no switch to worry about , unless you need to use an isolating switch , im not sure if you do or not.

 

[Carol]

No idea of the regs but we have a separate switch so the light can be on without the fan. The noise in the dead of night is not ideal and in the freezing winter it is no fun to bath with the fan going. House rule is "if you bath or shower the fan goes on straight afterwards."

Perhaps other people have warmer bathrooms!.

 

[Schoolmarm]

My daughter has the same situation where there is no power to make it overrun. It is the most important part of the fan's duties and I wish I knew how to get round it.

If somebody is quick or goes to get dried and dressed in another room I suppose the light could be left on.

 

[FamilyWiggs]

We have an opening window

We have an extractor fan vent in the ceiling, which doesn't work but provides a howling gale into the room - providing ventilation and motivation not to linger in there.

 

[Flyfisher]

if it were me and i was starting a fresh id install a fan with a movement sensor on it so it will come on when some one is in the room regardless of the time of day. i never really seen the point of an extractor that only works when you put the light on unless you have a very dark bathroom or one with no windows.

I'm not sure if there are bathroom-rated movement detectors available but, even so, they might not be too effective for a long soak in the bath or when in a shower cubicle.

A completely separate switch for the fan is a good idea, and is the arrangement we have with the upstairs bathroom, but this is just for a downstairs 'utility' shower room. Perhaps I'll have another look at the wiring tomorrow . . .

 

[Jill]

The bathroom fan overruns for quite a while after the light has been switched off but I've never timed it , i'll be having a shower soon so i'll time it for you.

1 minute 44 seconds - guess its not quite a while after all!

The switch on the outside is an isolator. (It says so on it).

 

[CatherineB]

Our fan, which gave up the ghost within months of being fitted (and we never bothered to get it fixed), has a dial on its control panel, which enables you to lengthen or shorten the time it stays on.

Do you need one for an internal stand-alone WC? Or utility?

 

[Schoolmarm]

Ah, FF, see you just need a dial, not an unswitched source. :lol: :lol:

 

[Flyfisher]

1m 44s seems like a short time, unless it's a very powerful fan. The regs suggest 15 minutes, presumably at the minimum specified ventilation rate of 15 litres/sec. The overrun fans I've seen all have a timer adjustment somewhere.

Yes, ventilation fans are now required for utility rooms and WCs. From what I've read the required rates are:

Kitchen (near hob) : 30 litres/sec
Kitchen (elsewhare) : 60 l/s
Utility : 30 l/s
Bathroom :15 l/s
WC : 6 l/s

These are all 'intermittent' ventilation rates, i.e from fans, but there are also 'continuous' ventilation requirements and it's interesting to note that the "whole house" continuous ventilation requirement for a typical 3-bedroom house is 21 litres/sec. That's 1260 litres of expensively-heated warm air being thrown out every minute and replaced with cold air from outside.



For anyone interested or suffering from insomnia, the details are here:
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADF_2006.pdf

 

[Flyfisher]

My daughter has the same situation where there is no power to make it overrun. It is the most important part of the fan's duties and I wish I knew how to get round it.

If somebody is quick or goes to get dried and dressed in another room I suppose the light could be left on.

Yes, my plan is to just leave the light on for 10-15 minutes or open the window after showering, although I'm hoping that having the extractor vent above the shower cubicle will mean that most of the steam will be extracted during the shower and not steam up the rest of the room too much. We'll see.

 

[Jill]

Our extractor vent is directly above the shower, tonight the mirrors didn't steam up at all, sometimes they do. The rates you have quoted are the same on our plans. I don't know if ours is a powerful fan or not as I don't have the leaflet. By the time I have got out the shower, dried, moisturised, faffed about with my hair (on my head, before Penners starts) then at least 10 - 15 mins has passed before the light is switched off, so the very short over run time doesn't really bother me.

 

[Penners]

Bathroom :15 l/s

When I got BR consent to install a bathroom, FF (about 5 yrs ago), my application plans showed the room as having a 15 l/s extractor fan (as well as a window). I got the consent without any query as to whether the fan had a run-on function.

Obviously I can't be sure whether the regs have been modified between then and now.

By the way, I did once have to install such a fan in a location where the run-on supply was very difficult to organise from the same junction box as the switched supply. I solved this by running the permanent run-on supply as a single feed from another junction box, some distance away. I don't know whether that's any help.

 

[Flyfisher]

Yes, helpful and consistent with everything I've found, or rather not found, regarding the regulatory need for an over-run, so I don't think I'll bother. It would be possible, of course (most things are with time and lots of fiddling about), but the existing wiring is such that the only power into the bathroom is a switched cable to the light itself. Thus, it's very easy to connect the fan to the light but there's no provision for over-running without a fair bit of extra wiring.

Anyway, as Jill has pointed out, by the time I've dried myself, moisturised, fixed my hair, shaved my legs and plucked my eyebrows, I'm sure all the steam will have cleared and it'll be fine for the fan to switch off with the light.

 

[AMc]

These are all 'intermittent' ventilation rates, i.e from fans, but there are also 'continuous' ventilation requirements and it's interesting to note that the "whole house" continuous ventilation requirement for a typical 3-bedroom house is 21 litres/sec. That's 1260 litres of expensively-heated warm air being thrown out every minute and replaced with cold air from outside.

For anyone interested or suffering from insomnia, the details are here:
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADF_2006.pdf

In an old house I'd be amazed if you got down to that volume of air exchanges as the building methods simply don't produce an air tight envelope.

In a new build whole house mechanical heating and ventilation systems with heat exchangers are increasingly common to warm incoming cold air with extracted warm air which makes the heat loss more bearable.

I did once read that a house specified to Passivhaus (designed for no direct heating) it would technically be possible to suffocate if the MHV system failed for an extended period of time. In practice I think that's very unlikely though

 

[Flyfisher]

In an old house I'd be amazed if you got down to that volume of air exchanges as the building methods simply don't produce an air tight envelope.

I quite agree.

But I do find it a little incongruous that there are regulations specifying the performance of windows, thereby completely eliminating SG windows, alongside regulations requiring the exhaust of 1260 litres of warm air every minute. I know that heat exchangers are increasingly used in new builds (and can, of course, be retrofitted at some cost and disruption), but I'm not aware of their requirements under any regulations, which seems a little inconsistent.

It would be interesting to know the typical figures for the heat loss saved by DG compared to SG windows against the heat lost by expelling 1260 litres of warm air every minute.

 

[AMc]

It would be interesting to know the typical figures for the heat loss saved by DG compared to SG windows against the heat lost by expelling 1260 litres of warm air every minute.

If you're not fitting MHV then you aren't explicitly chucking air out.

A sealed single glazed window (no draughts) and a sealed double glazed window (no draughts) would have no impact at all on that ventilation heat loss - the lower loss through conduction and radiation would make the DG window seem substantially better.
Of course a completely draught proof single glazed window isn't that likely and as dg replacements are generally mandated to have trickle vents then a draught is essentially introduced at roughly the rate to comply with the ventilation requirements.
IIRC the U value calculations for building elements are based on heat transfer from one side to the other in still air. I'd be academically interested to know if trickle vents are included in the heat loss assessment of replacement windows but somehow I doubt it.

I suspect (though have no source for) the trickle vent requirement is there to maintain ventilation for damp and condensation in older houses where replacement windows are fitted but no other work is in place. I can imagine that when the first installations of double glazed, plastic windows into older houses without vents resulted in some serious damp issues.


Heat recovery units can be included as part of a SAP "whole house" assessment which can be used to comply with building regs (L1A or L1B).
You produce a illustration for the dwelling using the defined elemental heat loss profiles for everything, then a second one showing that the give and take between what you are proposing produces a lower overall heat requirement.
In theory you could probably install single glazed windows as part of a new build or renovation that added above spec wall, floor, roof insulation and a 'green' heating system (log boiler, heat pump etc.) but I can't imagine anyone would want to.